Squat-to-stand provocation of dynamic left ventricular outflow tract obstruction in hypertrophic cardiomyopathy: a case report

Background Left ventricular outflow tract (LVOT) obstruction is an important determinant of the management of hypertrophic cardiomyopathy (HCM). With a nationwide shortage of amyl nitrite in 2019, we implemented a ‘repetitive squat-to-stand’ manoeuvre to provoke LVOT obstruction during echocardiography. Case summary A 64-year-old female was referred with symptomatic HCM refractory to pharmacologic therapy. Transthoracic echocardiography showed minor LVOT obstruction with conventional imaging at rest and during Valsalva manoeuvre, but severe obstruction was confirmed with the repetitive squat-to-stand manoeuvre. Alcohol septal ablation via the first septal perforator was performed with subsequent resolution of symptoms. Discussion Due to the dynamic nature of LVOT obstruction, a series of provocative manoeuvres including Valsalva manoeuvre, inhalation of amyl nitrite, and exercise are often necessary to maximally augment ventricular obstruction. The recent unavailability of amyl nitrite during a nationwide shortage prompted the implementation of a protocol of repetitive squat-to-stand manoeuvre in our echocardiography laboratory. Rising from the squatting position decreases preload and afterload, both of which augment dynamic LVOT obstruction. Repetition of squatting and standing appears to enhance the sensitivity of the manoeuvre, particularly when exertional symptoms are reproduced. In this case, repetitive squat-to-stand manoeuvre led to the identification of severe LVOT obstruction which may not have been diagnosed otherwise, alteration of treatment to septal reduction therapy, and subsequent resolution of symptoms.

Abstract 13876: Squat-to-stand Provocation of Dynamic Left Ventricular Outflow Tract Obstruction in Hypertrophic Cardiomyopathy

Background: Left ventricular outflow tract (LVOT) obstruction is an important determinant in management of hypertrophic cardiomyopathy (HCM). Valsalva maneuver and amyl nitrite are used in clinical practice during resting echocardiography to induce latent obstruction (LVOT gradient <30 mmHg at rest, ≥30 mmHg with maneuver). With a nationwide shortage of amyl nitrite in 2019, we implemented a “repetitive squat-to-stand” maneuver to provoke LVOT obstruction during echocardiography. Methods: Patients with known or suspected HCM without resting obstruction who underwent repetitive squat-to-stand maneuver during echocardiography between February and September 2019 were included. Maximal instantaneous gradients were recorded. Provocable gradients were compared utilizing a two-sided t-test. Amyl nitrite was not available during the study period. Results: Squat-to-stand assessments were available in 125 patients without resting obstruction (age 58 ± 15 years, 67% male); 114 also performed Valsalva maneuver. 47 of 125 patients (37.6%) demonstrated provocable obstruction. 46 (36.8%) demonstrated latent obstruction provoked by squat-to-stand, which was severe (gradient ≥50 mmHg) in 29 (23.2%). Of the 46 patients, 19 demonstrated latent obstruction only with squat-to-stand but not with Valsalva, 13 of which demonstrated severe obstruction. Among patients with latent obstruction who performed both Valsalva and squat-to-stand maneuver (n=41), squat-to-stand resulted in a higher gradient than Valsalva maneuver (p<0.0001, Figure). Conclusion: Repetitive squat-to-stand maneuver is a clinically useful adjunct to the traditional echocardiographic exam in HCM. This maneuver appears to be more sensitive than the Valsalva maneuver for identifying severe dynamic LVOT obstruction. Use of repetitive squat-to-stand warrants further study in comparison to amyl nitrite, particularly regarding cost savings and diagnostic performance.

Inhalants

Inhalants are a pharmacologically diverse group of substances with a common route of use. An estimated half million Americans are current inhalant users. Use is highest among adolescents and declines with age. Nitrous oxide is the most commonly used, followed by amyl nitrite and organic compounds. There are clues on history and examination that should raise the suspicion of inhalant use. Metabolites of some organic compounds can be detected on urine testing. Volatile organic compounds are found in a wide variety of household and industrial products. They are associated with a number of medical complications, the most serious of which is encephalopathy. Nitrous oxide and other volatile anesthetic agents are commonly used. The most serious complication associated with their use is hypoxia. Amyl nitrite and related compounds are potent vasodilators. The most serious complications associated with their use are hypotension and methemoglobinemia. There are few data on treatment of individuals who use inhalants.